The great brain debate - Ted Altschuler

Throughout history, scientists have proposed conflicting ideas on how the brain carries out functions like perception, memory, and movement. Is each of these tasks carried out by a specific area of the brain? Or do multiple areas work together to accomplish them? Ted Altschuler investigates both sides of the debate.

In 1861, two scientists got into
a very brainy argument.

Specifically, they had opposing ideas
of how speech and memory

operated within the human brain.

Ernest Aubertin,
with his localistic model,

argued that a particular region
or the brain

was devoted to each separate process.

Pierre Gratiolet, on the other hand,
argued for the distributed model,

where different regions work together

to accomplish all of these
various functions.

The debate they began reverberated
throughout the rest of the century,

involving some of the greatest scientific
minds of the time.

Aubertin and his localistic model
had some big names on his side.

In the 17th century, René Descartes
had assigned the quality

of free will and the human soul
to the pineal gland.

And in the late 18th century, a young
student named Franz Joseph Gall

had observed that the best memorizers
in his class had the most prominent eyes

and decided that this was due
to higher development

in the adjacent part of the brain.

As a physician, Gall went on to establish
the study of phrenology,

which held that strong mental faculties
corresponded to

highly developed brain regions, observable
as bumps in the skull.

The widespread popularity of phrenology
throughout the early 19th century

tipped the scales towards
Aubertin's localism.

But the problem was that Gall had never
bothered to scientifically test

whether the individual brain maps
he had constructed

applied to all people.

And in the 1840's, Pierre Flourens
challenged phrenology

by selectively destroying parts
of animal brains

and observing which functions were lost.

Flourens found that damaging the cortex

interfered with judgement or movement
in general,

but failed to identify any region
associated with one specific function,

concluding that the cortex carried out
brain functions as an entire unit.

Flourens had scored a victory
for Gratiolet, but it was not to last.

Gall's former student,
Jean-Baptiste Bouillaud,

challenged Flourens' conclusion,

observing that patients
with speech disorders

all had damage to the frontal lobe.

And after Paul Broca's 1861 autopsy of a
patient who had lost the power

to produce speech, but not the power
to understand it,

revealed highly localized
frontal lobe damage,

the distributed model seemed doomed.

Localism took off.

In the 1870's, Karl Wernicke associated
part of the left temporal lobe

with speech comprehension.

Soon after, Eduard Hitzig and
Gustav Fritsch

stimulated a dog's cortex and discovered
a frontal lobe region

responsible for muscular movements.

Building on their work, David Ferrier
mapped each piece of cortex

associated with moving a part of the body.

And in 1909, Korbinian Brodmann built
his own cortex map with 52 separate areas.

It appeared that the victory of Aubertin's
localistic model was sealed.

But neurologist Karl Wernicke had come up
with an interesting idea.

He reasoned that since the regions for
speech production and comprehension

were not adjacent,

then injuring the area
connecting them might result

in a special type of language loss,
now known as receptive aphasia.

Wernicke's connectionist model helped
explain disorders

that didn't result from the dysfunction
of just one area.

Modern neuroscience tools reveal a brain
more complex than

Gratiolet, Aubertin,
or even Wernicke imagined.

Today, the hippocampus is associated
with two distinct brain functions:

creating memories and processing
location in space.

We also now measure
two kinds of connectivity:

anatomical connectivity between
two adjoining

regions of cortex working together,

and functional connectivity
between separated regions

working together to
accomplish one process.

A seemingly basic function like vision

is actually composed
of many smaller functions,

with different parts
of the cortex representing

shape, color and location in space.

When certain areas stop functioning,
we may recognize an object,

but not see it, or vice versa.

There are even different kinds of memory
for facts and for routines.

And remembering something
like your first bicycle

involves a network of different regions
each representing the concept

of vehicles, the bicycle's shape,
the sound of the bell,

and the emotions associated
with that memory.

In the end, both Gratiolet and Aubertin
turned out to be right.

And we still use both of their models
to understand how cognition happens.

For example, we can now measure brain
activity on such a fine time scale

that we can see the individual localized
processes that comprise

a single act of remembering.

But it is the integration of these
different processes and regions

that creates the coherent memory
we experience.

The supposedly competing theories
prove to be two aspects

of a more comprehensive model,

which will in turn be revised and refined

as our scientific techologies and methods
for understanding the brain improve.